What you're trying to do isn't really possible, because you are breaking up the table structure in two. This means that each cell in the 2nd table (1,2,3..) is going to have the width of its' contents and won't be affected by the width of the header cells (Jan, Feb, Mar...).

This is why you're seeing this.

One way to fix this is by applying table-layout: fixed on both tables, and then giving each td a fixed width and the display: inline-block property.